Pneumatic tires are typically comprised of a tire carcass and a tread. The carcass has two or more layers of rubberized fabric or metal usually in a cord or cable form and provides the foundation structure for the tire. The carcass also has reinforcing sidewalls, and a pair of circumferential beads adapted to hold the tire on a rim of a wheel and pneumatically seal the tire with the wheel. The tread of rubber typically filled with carbon black, is integrated with the tire carcass and provides the ground-engaging surface of the tire. A breaker or belt assembly is also sometimes provided between the carcass and tread portion and, depending on the type of tire being built, may be assembled with either the carcass or the tread.
Pneumatic tires are categorized by whether the reinforcing cords in the plies of the carcass are radial or bias to the axial centerline of the tire. Tires of the bias type have been built by the "flat band" method utilizing equipment such as that described in U.S. Pat. Nos. 2,614,951, 2,614,952, 2,628,652, 3,171,769, 3,156,601 and 3,645,826, all of which are owned by the assignee of the present application. Typically, tires of radial type have been built by the "toric match" method utilizing a method and equipment such as that described in U.S. Pat. No. 3,475,254, which is also owned by the assignee of the present application.
The building techniques for building both radial and bias ply tires are similar in that the tires are built on one or more expansible cylindrical drums. In either case, building is commenced by placing one or more carcass plies around such an expansible building drum so as to form an annular flat band with edge portions of the band overhanging the ends of the drum. Then, the drum surface is uniformly radially expanded to a second diameter, to provide a bead ring receiving shoulder at each end of the drum. Thereafter, annular bead rings, which usually consist of essentially inextensible rubberized cords and/or wires, are abutted or seated against said shoulders by bead ring seating or carrier means; and the edges of the band are then wrapped, typically by inflatable, turnup bladders and annular pushover rings, around the bead ring and folded back on and stitched to the outer surface of the annular bands.
One of the primary difficulties with such expansible building drums has been that they provided no flexibility in their expansion. Whether expanded by an inflatable bladder, e.g. see U.S. Pat. No. 3,475,254, or by a mechanical drive, e.g. see U.S. Pat. No. 3,698,987, the expansible drum is either positioned at one of two diameter settings, i.e. the first diameter where the carcass plies are applied, and the second diameter where the beads are formed. There is no intermediate diameter settings possible. Further, there is no positive control or flexibility in the diameter settings for both expanding and contracting the drum.
Various diameter settings facilitate the building of certain pneumatic tires and particularly off-the-highway pneumatic tires. Off-the-highway tires are pneumatic tires of very large (or "giant") size and varied bead diameters for tractors, road graders, earthmovers and the like. Typically, only a few tires may be made of one diameter and then the production is changed to a tire of a different bead diameter. With known building machines, this change-over requires the use of different building drums: The production is shut-down for some hours while one drum is detached and another assembled in place. Furthermore, with such tires, it expedites the building operation if a portion of the carcass, e.g. subsequent plies and sidewalls, can be assembled with the building at an intermediate diameter or diameters between a first diameter at which the first carcass plies are applied and a second diameter at which the beads are formed and possibly the tread rubber applied.
Another difficulty with such expansible building drums is that an inflatable rubber bladder is utilized for at least a part of the expansion. Air and rubber are notoriously unstable in positioning and therefore dimensional stability of the drum is difficult to maintain. Maintenance of this stability is a particularly difficult problem with giant off-the-highway tires where high forces are needed especially in bending the construction material. A related problem is the expansion capability of existing building drums which limit the size of tires that can be made.